Some building construction techniques involve the application of a coating, such as stucco, to a surface. This coating is the cladding or the finish for such surfaces. In the following disclosure, the term “stucco” is used generally to apply to cementitious plasters or gypsum plasters, including stuccos as defined in applicable building codes.
When applying a coating of stucco, it is generally desirable to provide a lath on the surface. The lath provides reinforcement for the stucco and attaches the stucco to the vertical building surface.
The framing for buildings is typically constructed with wood or steel studs. In some situations, sheathing may be applied over the framing. This sheathing may be in the form of wood boards, plywood, oriented strand board (OSB), gypsum wall board, EPS foam or other types of sheathing material. In other situations, the framing is left open. Typically, a water resistant membrane, such as building paper or building wrap, is applied over the open framing or over the sheathing. The lath is then applied over the water resistant membrane.
The lath is attached to wood and metal framing by various fasteners, generally including nails, staples, self-tapping screws or other mechanical fastening means. Fastening is normally spaced every 6 inches in the vertical direction with framing 16 inches on center or every 4 inches in the vertical direction with framing 24 inches on center. With open frame structures, the lath must be attached to the frame elements. In the case of structures with sheathing, for structural purposes, it is still desirable to attach the lath to the frame elements. In these situations the fasteners must pass through the sheathing material first.
There are a number of different metal lath types being used for stucco coatings. One common type is expanded metal lath. Another group of stucco laths are wire fabric laths. Within this group there are woven wire laths and welded wire laths. This invention is specifically related to the welded wire lath group.
In the prior art, welded wire lath is provided in a variety of configurations, but it is comprised typically of a wire mesh of intersecting horizontal and vertical wires that are welded together at the intersections, defining a plurality of square or rectangular openings. Typically, mesh openings are 2 inches by 2 inches, 1½ inches by 1½ inches, or 1 inch by 1 inch.
Another requirement for stucco surfaces is that the lath be spaced away from the framing or sheathing to allow the stucco, when applied, to surround the lath and obtain sufficient keying and bonding. This spacing is achieved with the use of furring or spacing devices, such as furring nails, or with the application of self-furring laths. In the prior art as disclosed by Frank in U.S. Pat. No. 3,342,003, the mesh reinforcement has bent portions for spacing the mesh away from a substrate. However, one major disadvantage with the prior art as disclosed by Frank is that the bent portions are bent to form a ‘dovetail’ shape and the bent portions “are in contact with each other and rigidly secured together”. This requires a separate process which is difficult and costly to incorporate into a manufacturing process.
In the past, the most common construction practice has been wood framing with the lath attached by staples. The advantage of using staples is that the two legs of a staple can surround both sides of a horizontal wire and physically trap the lath to the structure. It would not be necessary to try and attach at an intersection of the lath.
However, the use of staples is now being discouraged for several reasons. First, each staple produces two holes in the moisture barrier membrane, whereas a nail or screw only produces one hole at each location. With the increasing problems of moisture entry into structures and the resulting material deterioration and mold concerns, there is a desire to reduce the number of penetrations through the moisture barrier membrane.
Secondly, steel framing is becoming more popular as wood framing becomes more expensive. Steel framing has typically been used in non load bearing commercial or high rise applications but, more recently, it is now being used to a greater extent in load bearing residential applications. Staples cannot be used with steel framing and self-tapping screws must be substituted. The screws must have a large head and must be applied at an intersection of the horizontal and vertical wires. This method of attachment for the lath is a problem because the lath is not securely attached to the structure. In some cases, the intersection of the lath does not coincide with the framing member. Furthermore, the lath is only being pinched under a part of the screw and it is not trapped, which may cause it to disengage with structural movement.
Thirdly, it was found that staples sheared off of structures in the Northridge earthquake in California in 1993 and that stucco claddings fell off of buildings. In those cases, stucco was also providing shear value to the structure and when the stucco came loose, the buildings suffered serious damage and collapse. As a result, various jurisdictions had banned the use of staples for attaching lath in seismic zones. Further, with prior art lath, it was found that there was inadequate embedment of the lath in the stucco and, as a result, there was delamination of the lath and stucco during the Northridge earthquake in Northridge Calif.
Rutherford in U.S. Pat. No. 3,991,536 discloses an improved welded wire fabric lath, which includes double strands of wire located at predetermined spaced intervals. The wires of the double strand are spaced slightly apart to provide a slot for receiving fasteners that are used to hold the lath in place on wood and metal framing. Rutherford states “that screw fasteners or nails can now be used, thus eliminating the use of other mechanical fasteners to attach the lathing and eliminating the perforations through the waterproof backing.”
In Rutherford's invention, the double strands are located at the furring location. As he clearly shows in his figures, the double strands are not in the same plane as the body of the lath. This results in two problems. First, as a result of this configuration, the lath cannot be rolled up and can only be produced in sheets. Secondly, the double strands are not furred away from the building frame and are not embedded by the stucco when it is applied.
A problem of economic importance is the method for packaging the lath; more specifically the ability of the lath to be rolled up for easy handling and shipping. Clancy in U.S. Pat. No. 617,458 and Jaenson in U.S. Pat. No. 5,540,023 describe wire mesh lathing material in which strands are welded at the furring location and therefore not in the plane of the lath. Consequently, this structure makes their laths impossible to be rolled up for any practical purposes.
Another invention described by Kreikemeier in U.S. Pat. No. 5,287,673 consists of a lath cast in plastic with furring consisting of bars. This structure makes it impossible for his lath to be rolled up in the direction of the bars.
In U.S. Pat. No. 6,305,432 Sacks describes a lath with flattened wires along one particular direction. This design which allows the lath to be rolled along that direction and therefore compactly packaged, can save significant costs in shipping and handling. Sacks' design however, does not have the slots structure as described by Rutherford.
Hence, there is a need for an improved welded stucco lath that provides positive attachment with nails or screws. The welded lath should also be manufactured in rolls, it should be self furring, and all the horizontal wires should be in the proper plane.
It is therefore an object of this invention to provide a self-furring lath equipped with slots comprising closely spaced parallel strands welded to the lath, wide enough to allow the insertion of fastener's shafts, yet narrow enough to hold the fastener's heads and to further provide a lath with these closely spaced parallel strands which are furred away from the building frame.
It is a further object of this invention to describe a lath with closely spaced parallel strands, that can be compactly rolled for easy and economical handling and shipment.